Method for functionalization of polyolefins

ABSTRACT

A method for modifying polyolefins by grafting with a carboxylic acid, carboxylic acid anhydride or other functionalized monomer in the presence of two additional comonomers, one being an aliphatic diolefin and the other an aromatic vinyl or (meth)acrylate monomer.

The invention relates to a method for the functionalization ofpolyolefins in molten state so that the obtained product, as such ormelt-mixed with other polyolefins, will achieve good adhesion with otherpolymers, metals, or other inorganic materials. The invention relatesboth to a method for the preparation of functional polyolefins and tomulti-layer products and mixtures of a functional polymer with otherpolymers and/or an inorganic substance, prepared by using the method.

The grafting of a functional unsaturated monomer onto polyolefins, inparticular onto polypropylene, can be carried out by at least threedifferent technologies.

The grafting can be carried out at a temperature below the meltingtemperature of the polymer, for example in a fluid-bed reactor. In thiscase, a very long reaction time can be selected, thus making possible ahigh conversion of the monomer. Any ungrafted monomer can be removed byvacuum stripping (U.S. Pat. No. 3,414,551).

Another prior known method is based on solution or suspension grating,in which the polymer is grafted in a hydrocarbon solvent, in general ata temperature of 80°-160° C. Any unreacted monomer can be rinsed offwith alkali-containing water (EP 202 921, U.S. Pat. No. 4,698,395).

A third commonly used method is grafting in molten state, e.g. in asingle- or twin-screw extruder. This method has the disadvantages thatthe reaction time is limited and the reaction temperature is higher thanin the above methods, and therefore the conversion usually remainsrather low and the breaking up of polymer chains is considerable. Theamount of free monomer can in part be reduced by means of vacuum suctionor extraction methods, but these methods are usually ineffective and/orexpensive.

German patent publication DE 2 023 145 discloses a method in which thegrafting of a maleic acid anhydride onto a polymer can be enhanced byusing as an aid one vinyl monomer. However, the method has thedisadvantage that the amount of vinyl monomer required is high. Theadhesion properties of the product are not reported.

European patent application EP 280 454 discloses a method in which, inaddition to the functional monomer, a second monomer, for examplestyrene, is used in the grafting which copolymerizes under the effect ofheat. The "grafting reaction" is performed in the absence of peroxideinitiators which produce polymer radicals. The polyolefin used must notcontain antioxidants.

Epoxy functionalization of ethylene-propylene rubber andethylene-propylene-diene rubber is disclosed in patent application EP274 744. According to it, the functionalization is performed with theaid of a peroxide initiator by using, for example, glycidyl acrylate asthe functionalizing agent.

The present invention is characterized in that a polyolefin is graftedwith a functional monomer and, in addition, two comonomers are used, ofwhich one is an aliphatic (di)olefin and the other is an aromatic vinylmonomer or (meth)acrylate monomer.

The polymer to be functionalized is a polyolefin, such as a homo-, co-or terpolymer of ethylene, propylene, butene, or 4-methyl-pentene.

The functional monomer is an unsaturated carboxylic acid having acarbon-carbon double bond, a carboxylic acid anhydride, or some othercarboxylic acid derivative such as carboxylic acid ester. Also an imide,either as such or imidized in situ from an anhydride, belongs to thisgroup. Especially recommended are α-unsaturated carboxylic acids,corresponding anhydrides, and epoxy-, amino- and hydroxy functional(meth)acrylates. The amount of the functional monomer is 0.1-10% byweight, preferably 0.2-5% by weight, of the amount of the polymer.

In addition to the functional monomer the method of the invention usesso-called co-monomers, which can be divided into two categories: (1)aliphatic diolefins such as C₆ -C₁₈ α-olefins, preferably 1-octene, and(2) aromatic vinyl monomers and (meth)acrylates, preferably styrene orparamethyl styrene or buty acrylate. The combined total amount of thecomonomers is 0.01-30% by weight, preferably 0.1-10% by weight, of theamount of the polymer.

Free-radical initiators are used for the production of polymer radicals.Free-radical initiators are often peroxides, such as diacyl peroxides,dialkyl peroxides, peroxy acids, peroxy esters, hydroperoxides, andalpha-oxy- and alpha-peroxyhydroperoxides or -hydroperoxides. Otherfree-radical initiators that should be mentioned include azo-compounds,N-nitrosoanilides, and combinations of dialkyl peroxides with silanes.The initiator is typically fed directly into the melt-mixing apparatus,but can also be mixed in advance with polymer pellets. The amount of theinitiator to be used is affected, for example, by the amount ofadditives present in the polymer. In general, initiator is used in anamount of 0.01-2% by weight of the amount of the polymer to befunctionalized.

The grafting reaction is performed in molten state by using a twin-rollmill, a Banbury mixer, or a single- or twin-screw extruder. Therecommended reaction temperature is 160°-260° C., and the reaction timeis at minimum 15 seconds. According to a preferred embodiment, thepolymer or the polymer mixture, the functional monomer, and at least aportion of the comonomer (1) and the peroxide are fed in at the initialstage of the reaction. The comonomer (2) may be fed in simultaneously oreven considerably later, depending on the desired properties of the endproduct.

The disadvantages of the state-of-the-art methods, such as lowconversion and deleteriously high breaking up of the polymer chains(polypropylene) can be avoided by the method according to the presentinvention. By the method according to the invention, an effectiveconversion of the functional monomer, a controlled change in the meltindex, easy compounding, insignificant change of color of the basicpolymer, and excellent properties of the end product are achieved.

The product of the invention can be used as an adhesion plastic or itscomponent, as a compatibilizer of polymer mixtures, as a coupling agentbetween polymers and inorganic materials, as a reducer of the migrationof stabilizers, and as an improver of the dyeability and paintability ofpolymers.

The invention is described in greater detail with the help of thefollowing examples.

The conversion of maleic acid anhydride in a twin-screw extruder in theabsence of comonomers is typically approx. 30%. This can also be seen inComparative Examples 1 and 2. When the method according to the inventionis used, the conversion of maleic acid anhydride is 65-86%, as can beseen in Examples 3-8. Examples 9-13 show the excellent adhesion andcompatibilizing properties of the functional polymer prepared by themethod of the invention. In example 14, the invention is compared withthe functionalization methods disclosed in patent applications DE 2 023154 and EP 280 454.

EXAMPLE 1 (Comparative Example)

A homopolypropylene powder (melt index MFR=1.9, manufacturer NesteChemicals) was grafted with maleic acid anhydride (MAH) is a BerstorffZB25*39.5D twin-screw extruder by using a temperature profile of160°-200° C. The amount of maleic acid anhydride fed in was 1.5%. Theinitiator used was 0.1% of 1,3-bis(tert-butylperoxy-isopropyl)benzene(Perkadox 14S, Akzo Chimie BV). The total and free acid contents in theend product were determined by titration.

The conversion of the maleic acid anhydride was 31%, and the amount offree acid was 1.06%. The melt index (MFR) of the product was 108. Thecolor of the product was brownish.

The test results of Examples 1-8 are compiled in Table 1 after Example8.

EXAMPLE 2 (Comparative Example)

The experiment according to Example 1 was repeated by using, instead ofhomopolypropylene, a random copolypropylene which had ethylene as acomonomer and which had a melt index of 1.8 and a typical melting point(DSC) of 142°-144° C. (manufacturer Neste Chemicals).

EXAMPLE 3

The experiment according to Example 1 was repeated by using additionally0.75% of 1-octene and 0.75% of styrene. The comonomers were fed in atthe beginning of the reaction.

EXAMPLE 4

The experiment according to Example 2 was repeated by using in the feedadditionally 0.75% of 1-octene and 0.75% of styrene. The comonomers werefed in at the beginning of the reaction.

EXAMPLE 5

The experiment according to Example 1 was repeated by using additionally1.5% of 1-octene and 1.5% of styrene.

EXAMPLE 6

The experiment according to Example 1 was repeated, but by usingglycidyl methacrylate instead of maleic acid anhydride and additionally1.5% of 1-octene and 1.5% of styrene.

EXAMPLE 7

The experiment according to Example 1 was repeated by using additionally1.5% of 1-decene and 1.5% of paramethyl styrene.

EXAMPLE 8

The experiment according to Example 1 was repeated by using in the feed3% of maleic acid anhydride and additionally 3% of 1-octene and 3% ofstyrene.

The test results of Examples 1-8 show that the adding of comonomersimproves the conversion of the maleic acid anhydride considerably anddecreases the amount of free acid in the end product. The increasing ofthe comonomer concentration improves the results, but a considerableimprovement is achieved even with low concentrations. The color of theproduct remains good, i.e. the product is colorless, when the graftingis carried out by the method according to the invention.

                  TABLE 1                                                         ______________________________________                                        Properties of functionalized polymers                                         MAH conversion   Free acid                                                    (%)              (%)      MFR      Color                                      ______________________________________                                        Example 1                                                                            31            1.06     108    brownish                                 Example 2                                                                            31            0.58     128    brownish                                 Example 3                                                                            66            0.28                                                     Example 4                                                                            67            0.26                                                     Example 5                                                                            65            0.06     27     colorless                                Example 6                                                                            --            --       21     colorless                                Example 7                                                                            78            0.06     18     colorless                                Example 8                                                                            86            0.09     24     colorless                                ______________________________________                                    

EXAMPLE 9

The product according to Example 5 was melt-mixed with ahomopolypropylene (VB19 50K, manufacturer Neste Chemicals) and anethylene-propylene elastomer (Keltan 740P, DSM Elastomers) at the ratioof 25/50/25%. The amount of free styrene measured in the end product was5 ppm.

The adhesive of the obtained product was tested by using it as anadhesion layer between an expoxy-coated (Eurokote 714.32, BitumesSpeclaux) steel sheet and a heterophase polypropylene (SA40 20G, NesteChemicals) used as the surface material. The thickness of the surfacelayer was 1800 μm and the thickness of the adhesive layer was 200 μm.The number of steel sheets was 7 and their temperatures varied withinthe range of 175°-220° C. The adhesion was higher than the tensilestrength of the surface material (270-320N/cm).

EXAMPLE 10

The product according to Example 1 was melt-mixed with ahomopolypropylene (VB19 50K, Neste Chemicals) and an ethylene-propyleneelastomer (Keltan 740P, DSM Elastomers) at the ratio of 25/50/25%. Theamount of free acid measured was 0.18%.

When the above experiment was repeated by using additionally 0.3% ofn-butyl acrylate and 0.2% of octadecene and 0.02% of a peroxideinitiator (Perkadox 14S, Akzo Chimie BV), the amount of free acidmeasured was 0.08%. When styrene was used instead of n-buty acrylate,the amount of free acid was the same, 0.08%.

Of the last-mentioned material, a 5-layer laminate 900 mm wide wasprepared on an Er-We-Pa flat board line. The structure of the laminatewas homopolypropylene/adhesion plastic/ethylene-vinyl alcohol polymer(EVAL F101, Kuraray Co, Ltd)/adhesion plastic/homopolypropylene. Thethicknesses of the layers were 450/45/65/45/450 μm. The processingtemperatures of the materials were 220°-250° C. The inter-layer adhesionmeasured was 40N/cm.

When the experiment was repeated by using commercial adhesion plasticsAdmer QF 500 E (Mitsui Petrochemical Industries) and Modic P300F(Mitsubishi Petrochemical Industries), the adhesions obtained were11N/cm and 34N/cm.

EXAMPLE 11

The product according to Example 6 was melt-mixed in a BerstorffZE25*33D twin-screw extruder with a polybutene terephthalate (CrastinS600, Ciba-Geigy Marienberg GmbH) and a homopolypropylene (VC12 12H,Neste Chemicals) at the ratio of 4/20/76% by using zone temperatures of240° C. and a screw velocity of 200 rpm. A comparative experiment (Run2) was performed by using, instead of the product of Example 6, acommercial compatibilizer Exxelor PO 1015 (EXXON). Test bars wereprepared from the material by means of a Krauss-Maffei KM 60-210B2injection press by using zone temperatures of 230°-250° C. and a moldtemperature of 65° C. The mechanical properties of the materials weretested according to ISO/R527.

The results are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Mechanical properties                                                                        Run 1         Run 2                                            Compatibilizer Product of Example 6                                                                        Exxelor PO 1015                                  ______________________________________                                        Yield strength, MPa                                                                          36.8          34.4                                             Tensile elastic modulus, MPa                                                                 1890          1760                                             ______________________________________                                    

EXAMPLE 12

Glassfiber-reinforced materials were melt-mixed in a Berstorff ZE25*33Dtwin-screw extruder by using zone temperatures of 240° C., a screwvelocity of 160 rpm, and a polymer feed of 5.5 kg/h. The glassfiber wasfed into zone 4.

The commercial products used were:

PP=homopolypropylene, VC12 12H, Neste Chemicals

Glassfiber=Vetrotex 5137, Vetrotex International

PBT=polybutene terephthalate, Crastin S600, Ciba Geigy Marienberg GmbH

Compatiblizer=a chemically modified polypropylene, Exxelor PO X1, EXXON

Four trial runs were performed, in which the following feed compositionswere used:

Run 1: 76% PP, 20% glassfiber, 4% Exxelor compatibilizer

Run 2: 36.4% PP, 26% PBT, 35% glassfiber, 2.6% product of Example 5

Run 3: 36.4% PP, 26% PBT, 35% glassfiber, 2.6% product of Example 6

Run 4: 65% PBT, 35% glassfiber

Test bars were injection molded from the materials by means of aKrauss-Maffei KM 60-210B2 injection press by using zone temperatures of245°-255° C. and a mold temperature of 80° C. The strength and rigidityvalues of the test bars are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                        Strength and rigidity values                                                               Run 1   Run 2     Run 3 Run 4                                    ______________________________________                                        Tensile strength, MPa                                                                       81      90        89    80                                      Bending modulus, MPa                                                                       4780    9340      9800  9500                                     ______________________________________                                    

As can be seen from the results, the polymers according to the inventionwork very well as coupling agents between glass and polymer.

EXAMPLE 13

Compatibilization was investigated further by melt-mixing, in aBerstorff ZE25*39.5D twin-screw extruder, polymer mixtures whichcontained 57% of a homopolypropylene (VC12 12H, Neste Chemicals), 38% ofpolyamide-66 (Grilon T300GM, EMS Chimie AG), and 5% of a compatibilizer.The compatibilizers used were the polymer according to Example 5 (Run 1)and, on the other hand, a commercial chemically modified polypropylenerecommended for compatibilization (Exxelor PO XI 1015, EXXON). Theproperties of the polymer mixtures are compared in Table 4.

                  TABLE 4                                                         ______________________________________                                        Compatibilization of a mixture of polypropylene and polyamide                             Run 1          Run 2                                              Compatibilizer                                                                            According to Example 6                                                                       Exxelor PO XI 1015                                 ______________________________________                                        Tensile elastic                                                                           2320           2310                                               modulus MPa                                                                   Yield strength MPa                                                                        46             44                                                 Elongation at yield %                                                                     5.6            5.7                                                HDT (0.46 MPa) °C.                                                                 117            112                                                ______________________________________                                    

EXAMPLE 4

Polypropylene (melt index MFR=3.2, Neste Chemicals) was grafted in aBerstorff ZE25*33D twin-screw extruder by using a temperature profile of160°-200° C. and a screw velocity of 200 rpm. The components used in theexperiments were pre-mixed in a barrel mixer before being fed into zone1 of the extruder.

Run 1 was carried out in accordance with Patent EP 280 454, in theabsence of free-radical initiator by using 1.5% of maleic acid anhydrideand 0.75% of paramethyl styrene.

Run 2 was carried out in accordance with Patent DE 2 023 154 by using0.05% of Perkadox 14S free-radical initiator, 1.5% of maleic acidanhydride, and 0.75% of paramethyl styrene.

Run 3 was carried out in accordance with the invention by using 0.05% ofPerkadox free-radical initiator, 1.5% of maleic acid anhydride, 0.75% ofparamethyl styrene, and 0.75% of octadecene.

Run 4 was also carried out in accordance with the invention, as Run 3,but additionally 1500 ppm of Irganox B215 (Ciba Geigy) antioxidant wasused.

The amount of unreacted maleic acid anhydride (MAH) was analyzed byextracting from a ground polymer sample the free MAH in boilingisopropanol and by titrating the extraction solution with potassiumhydroxide. The results are shown in Table 5. The results show that, whenthe method according to the invention used, the amount of free maleicacid anhydride is clearly smaller and the use of antioxidants does notinterfere with the grafting.

                  TABLE 5                                                         ______________________________________                                        Amount of free maleic acid anhydride                                                     Free MAH, %                                                        ______________________________________                                               Run 1 0.82                                                                    Run 2 0.48                                                                    Run 3 0.37                                                                    Run 4 0.25                                                             ______________________________________                                    

I claim:
 1. A method for preparing a modified polyolefin by grating ontoit in molten state an unsaturated carboxylic acid, a carboxylic acidanhydride or carboxylic acid ester as the functional monomer, wherein inaddition to the functional monomer, two comonomers are used of which oneis an aliphatic monoolefin or aliphatic diolefin and the other anaromatic vinyl monomer or (meth)acrylate monomer.
 2. A method accordingto claim 1, wherein the amount of the functional monomer is 0.1-10% byweight of the amount of the polyolefin.
 3. A method according to claim1, wherein the combined total amount of the comonomers is 0.01-30% byweight of the amount of the polyolefin.
 4. A method according to claim1, wherein the aliphatic monoolefin is a C₆ -C₁₈ α-olefin.
 5. A methodaccording to claim 1, wherein the aromatic vinyl monomer is styrene orpara-methyl styrene.
 6. A method according to claim 1, wherein the(meth)acrylate monomer is alkyl (meth)acrylate.
 7. A method according toclaim 1, wherein the functional monomer is maleic acid anhydride.
 8. Amethod according to claim 1, wherein the functional monomer is glycidyl(meth)acrylate.
 9. A method according to claim 1, wherein the polyolefinis a homo-, co- or terpolymer of ethylene, propylene, butene or4-methylpentene.
 10. A modified polyolefin onto which has been graftedin the molten state 0.1-10% by weight of an unsaturated carboxylic acid,carboxylic acid anhydride or carboxylic acid ester, wherein inconnection with the molten-state grafting, there has been cografted analiphatic monoolefin or aliphatic diolefin and an aromatic vinyl monomeror (meth)acrylate monomer, the total combined amount of which is0.01-30% by weight of the amount of the polyolefin.
 11. A process ofusing a modified polyolefin prepared according to any one of claims 1-9as an adhesion plastic or its component, as a compatibilizer, or as acoupling agent between polymers and inorganic materials.
 12. A processof using a modified polyolefin according to claim 10 as an adhesionplastic or its component, as a compatibilizer, or as a coupling agentbetween polymers and inorganic materials.
 13. The method according toclaim 2, wherein the amount of the functional monomer is 0.2-5% byweight.
 14. The method according to claim 3, wherein the combined totalamount of the comonomers is 0.1-10% by weight.
 15. The method accordingto claim 4, wherein the C₆ -C₁₈ α-olefin is 1-octene or 1-decene.